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Particle size distribution (Granulometry)

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Endpoint:
particle size distribution (granulometry)
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
test procedure in accordance with generally accepted scientific standards and described in sufficient detail
Qualifier:
equivalent or similar to
Guideline:
ISO 13320 (Particle size analysis - Laser diffraction methods)
Version / remarks:
2009
GLP compliance:
no
Type of method:
Laser scattering/diffraction
Type of particle tested:
primary particle
Remarks:
dispersed in 0.1% Na-P-solution in dest. water
Type of distribution:
volumetric distribution
Key result
Percentile:
D90
Mean:
1.363 µm
St. dev.:
0.033
Key result
Percentile:
D50
Mean:
0.594 µm
St. dev.:
0.006
Key result
Percentile:
D10
Mean:
0.201 µm
St. dev.:
0.012
Conclusions:
The D 50 is given to be 0.594 um
Endpoint:
particle size distribution (granulometry)
Remarks:
Dustiness
Type of information:
experimental study
Adequacy of study:
supporting study
Study period:
2019
Reliability:
1 (reliable without restriction)
Rationale for reliability incl. deficiencies:
guideline study
Remarks:
Heubach-Dust-Meter connected to a cascade impactor
Qualifier:
according to
Guideline:
DIN 55992-1 (Determination of a parameter for the dust formation of pigments and extenders - Part 1: Rotation method)
Version / remarks:
2006
Deviations:
yes
Remarks:
a seven stage cascade impactor is connected to a heubach dust meter
Principles of method if other than guideline:
The Heubach dust meter is modified in a way that a seven stage cascade impactor is connected to the system. This involves an additional air fed of 20 L/min via the coarse dust separator needed to supply the cascade impactor with 40 L/min air current as specified in the manufacturer’s specifications.

The calculation report: EBRC (2017)
The Multiple-Path Particle Dosimetry Model (MPPD, v2.1; CIIT, 2009) was used to predict this fractional deposition behaviour for workers.
The model algorithms calculate the deposition (and clearance) of mono-disperse and polydisperse aerosols in the respiratory tract for particles ranging from ultra-fine (0.01 microns) to coarse (20 microns) sizes. Within each airway, deposition is calculated using theoretically derived efficiencies for deposition by diffusion, sedimentation and impaction within the airway or airway bifurcation. Filtration of aerosols by the head is determined using empirical efficiency functions.
GLP compliance:
no
Type of method:
rotating drum method
Remarks:
connected to a seven stage cascade impactor
Type of distribution:
volumetric distribution
Mass median aerodynamic diameter:
61 µm
Geometric standard deviation:
1.96
Remarks on result:
not measured/tested
Remarks on result:
not measured/tested

Dustiness (airborne fraction):      total: 269.93 mg/g.

In the original study report by DMT, the mass median diameter was not calculated. Since the deposited fractions were provided for each of the cascade impactor stages, it was possible to fit a bimodal lognormal distribution to the data by standard non-linear regression procedure. The weighting factors p, the MMADs and GSDs were calculated as follows:      

MMAD = 61.0 µm, GSD = 1.96

As the cascade impactor already takes aerodynamic characteristics of the particles into account, the reported mass median diameter can be interpreted as the mass median aerodynamic diameter.

These data and the corresponding GSD were used as distribution parameters for the MPPD model (v3.04) enabling an estimation of deposited dust fractions in the human respiratory tract: These fractions were estimated as follows:

Head (ET): 18.17 %

Tracheobronchial (TB): 0.02 %

Pulmonary (PU): <0.01 %

Conclusions:
Dustiness (airborne fraction):      total: 269.93 mg/g.

MMAD = 61.0 µm, GSD = 1.96;

Fractional deposition in human respiratory tract (MPPD model, based on calculated MMAD):

Head (ET): 18.17 %
Tracheobronchial (TB): 0.02 %
Pulmonary (PU): <0.01 %

Description of key information

Particle size distribution (PSD):

D (v, 0.1) = 0.201 μm

D (v, 0.5) = 0.594 μm

D (v, 0.9) = 1.364 μm

Dustiness:

- total dustiness (airborne fraction): 269.93 mg/g

Mass median aerodynamic diameter:

MMAD = 61.0 µm, GSD = 1.96

Fractional deposition in human respiratory tract (MPPD model, based on calculated MMADs):

Head (ET): 18.17 %

Tracheobronchial (TB): 0.02 %

Pulmonary (PU): <0.01 %

Additional information

The so-called physical particle size distribution (PSD) was obtained by the laser diffraction method in a wet dispersion after ultrasonic treatment for individualisation of the particles and further mechanical stirring. The particle size of the individualised particles is provided.

It is noted that any agglomerates of particles normally existing in the powder were destroyed by (i) the contact with water, (ii) the ultrasonic treatment and (iii) the mechanical stirring. Such agitation of the dry powder does however not occur under intended and foreseeable manufacture and use conditions and is therefore not suitable to deduce the likelihood of inhalation exposure under workplace conditions.

 

A suitable method for determining the PSD of a dry powder to assess the inhalation potential of airborne dust resulting from the handling of that powder is cascade impactor testing (Dustiness). During the cascade impactor testing, the material gets moderately agitated in a rotating drum (to simulate agitation during typical occupational powder handling activities). A constant airstream directs any generated airborne dust to a cascade impactor in which the particles and their agglomerates get separated according to their size.

The aerodynamic PSD is described as being bimodal.With the given parameters it is possible to calculate the cumulated mass percentage of particles at or below 4 µm. This fraction does however not indicate how much is deposited in the deep lung if such aerosol would be inhaled. Instead, the fractional deposition in the human respiratory tract was calculated using the MPPD model.

Thus, only a sub-fraction of the inhalable material (airborne fraction of < 0.01%) could deposit in the alveoli of the human lung.